Charge tube end plate

ABSTRACT

An end plate for securing and orienting a charge tube within a downhole-perforating gun. The end plate includes apertures for receiving locating tabs on the end of the charge tube to ensure the end plate is affixed to the charge tube in a specific orientation. The end plate includes an alignment tab that mates with a corresponding alignment groove in the perforating gun barrel for ensuring insertion of the charge tube into the perforating gun barrel in correct orientation to ensure the perforating charges exit through pre-designed scallops in the perforating gun barrel. A series of apertures may be present within the end plate to allow usage with one of a variety of sizes of charge tube. The end plate may include manipulation spaces along the circumference of the end plate to allow the end plate to be properly positioned or retrieved. The end plate may include an attachment system for attachment of an initiating device.

FIELD OF THE INVENTION

The present invention relates generally to well perforation tools. More particularly, the present invention relates to an end plate for securing a charge tube within the barrel of a perforating gun. More particularly, the present invention relates to an end plate for securing a charge tube within the barrel of a perforating gun having an attachment system for an initiating device.

BACKGROUND OF THE INVENTION

During the production life of an oil or gas well, it often becomes necessary to perforate the well casing and cement liner of the well in order to obtain access to further deposits within the formation. Several technologies have been developed for this purpose, including the use of downhole explosives, which are generally shaped charges placed and targeted to perforate the casing at a specific well depth and in a specific pattern. Generally, a “gun” containing a series of tailored shaped explosive charges, and a firing head are either run on wireline or attached to the bottom of a tubing string and so lowered to the target perforation depth. An electrical charge or a mechanical stimulus such as air or water pressure, depending on whether run on wireline or tubing, is applied to the firing head in order to detonate the charge.

In the downhole explosive industry, several sizes of gun barrels and charge tubes are manufactured to best fit several relatively standard casing and tubing sizes which define the bore of the well, and different situations require particular combinations of barrel and charge tube, depending on the downhole formation, and on the type of perforation desired. The standard sizes of gun barrels are designed to fit well bores of standard inside diameter, including: 4½″, 5½″, 7″, 9⅝″, 10¾″, 13⅜″, etc., inner diameter well bores. The standard outside diameter of suitably matched guns would be 3⅛″, 3⅜″, 4″, 4½″, 5″, 6″, 7″, etc. Normally, the largest gun that fits is used, but often a smaller gun will be used, particularly in the larger well bores. For example, a 5″ gun is often used for a 7″ or a 9⅝″ well bore. Likewise, various sizes and configurations of charge tubes are known, which may be customized for the type and number of charges required. The charge tubes, which carry and locate and align or aim separate shaped charges within the gun's barrel are necessarily of smaller diameter so as to fit inside, and are required to be easily assembled in proper alignment in a safe and convenient, yet secure assembly.

When the gun is assembled, the shaped charges are loaded into the charge tube, and the charge tube is located in the carrier and locked with an end collar ensuring that the charges align with pre-configured weak points or scallops in the gun. As the charge tube may be substantially smaller in diameter than the gun barrel, centralizers are often used to properly support the charge tube within the barrel. The end collar serves a triple function of securing the charge tube within the gun barrel, orienting the charge tube within the gun barrel, and providing a conduit for communication with adjacent downhole charges or with the surface of at least the detonation initiator, which is often a primer cord. An example of previous end collars can be found in Canadian Patent 2,243,178 to Buzinsky, which discloses both traditional aluminum molded end collars with set screws and threads for attachment to the charge tube, and also discloses threaded disks for the same purpose.

Due to the large size and weight of each component to be assembled (charge tube, perforating charges, and gun barrel), proper alignment of components during assembly is critical, however misalignment can often go undetected due to shearing of the aluminum alignment mechanism during accidental misassembly. Misalignment of a charge tube within the gun barrel may cause gun failure, resulting in a poorly fractured formation which may or may not be detected, or damage to the tubing or casing. Moreover, if the formation is poorly fractured, and reperforation is an option, it may be difficult, if not impossible, to retrieve the now misshapen gun components from their downhole location (in a worst case scenario).

Misalignment is particularly common when loading a 5″ and larger diameter gun barrel, as the industry standard for these larger guns includes a “Stub Acme Thread” or “½ Standard Full Acme Thread” threaded portion through which a channel is journalled, broached, or ground away, providing a groove to mate with a tab on the aluminum end collar. Due to the minimal threading depth, the depth of the alignment slot is limited, which in turn limits the size and effectiveness of the mating alignment tab on the aluminum end collar of the prior art. The charge tube and end collar can therefore be easily forced into the gun barrel even when not properly oriented.

An additional disadvantage to current end collars is cost. Most end collars are designed to accommodate a given size of charge tube and a given size of gun barrel. Therefore, a substantial inventory of end collars must be kept on hand. As the end collars are manufactured by casting or machining, the cost of current end collars is relatively high, including the cost of dies and molding equipment and special machinery.

U.S. Pat. No. 6,662,883 to Bonkowski discloses non-threaded end plates including axial slots for receiving engagement members for mechanical attachment of the end plate to the charge tube. The engagement members are either hooked members, or are deformable to engage the slots. This mechanical engagement, while having the advantage of simple assembly, introduces disadvantages to the system by providing movable and deformable parts, reducing the integrity of the system. In addition, it does not sufficiently address the issue of misalignment. It is susceptible to insecure assembly by reliance on deformed tabs, and provides little room for manipulation during the assembly process, which often takes place in the field.

It is, therefore, desirable to improve the assembly and loading of perforation guns to minimize gun failure as well as to minimize production costs.

SUMMARY OF THE INVENTION

It is an object of the present invention to obviate or mitigate at least one disadvantage of previous perforating gun assembly systems.

In one aspect, the present invention provides an end plate for use in the assembly of a perforating gun, the end plate having a plate member having an outer perimeter adapted to be slideable within a perforating gun barrel, and an alignment system without the outer perimeter adapted for mating in specific orientation with the inner surface of the perforating gun barrel, the plate member having one or more alignment apertures for aligning and mating with one or more corresponding locating tabs of a charge tube.

Preferably, the one or more alignment apertures are arranged asymmetrically. Preferably, a portion of the outer perimeter is recessed, providing a gap to permit the passage of gas past the end plate when the perforating gun is assembled, or to facilitate retrieval of the end plate and charge tube from the perforating gun barrel. Preferably, the one or more alignment apertures comprise a series of apertures for mating with the locating tabs of one of a variety of sized charge tubes. Preferably, the plate member comprises a plate passage to permit passage of an initiating device. Preferably, the passage comprises a central bore. Preferably, the initiating device comprises a detonating cord. Preferably, the alignment system comprises an alignment tab extending from the outer perimeter of the plate member and a corresponding alignment groove within the inner circumference of the perforating gun barrel. Preferably, the end plate includes an attachment system for attachment of an initiating device. Preferably, the attachment system comprises a puck adapted to attach to the end plate, the puck having a threaded aperture having a compression chamber, the aperture adapted to receive a compressible member and a threaded tube, wherein tightening the threaded tube into the threaded aperture compresses the compressible member in the compression chamber to frictionally engage the initiating device. Preferably, the compressible member is a cylindrical member having a central passage for passage of the initiating device, or is an o-ring.

In another aspect, the present invention provides a process for assembling a perforating gun including the steps of obtaining a charge tube with open ends, the charge tube loaded with charges and having an arrangement of locating tabs on at least one of the open ends; providing an end plate slideable within a perforating gun barrel and having a corresponding arrangement of alignment apertures for mating with the locating tabs, the end plate also having an alignment system for mating in specific orientation with the inner surface of a perforating gun barrel, affixing the end plate against the end of the charge tube such that the locating tabs mate with the alignment apertures; and inserting the charge tube and end plate into the perforating gun barrel such that the alignment system properly orients the end plate and the charge tube within the perforating gun barrel to align the charges with weakened or scalloped portions of the perforating gun barrel.

Preferably, the arrangement of locating tabs is asymmetrical.

In another aspect, the present invention provides a universal end plate for use in the assembly of a perforating gun, the end plate including a plate member having an outer perimeter slideable within a perforating gun barrel, an alignment system included in the outer circumference for mating in specific orientation with the inner surface of the perforating gun barrel; the plate member having at least two sets of alignment apertures, each set of apertures including one or more apertures for mating with corresponding locating tabs of one of a variety of sized charge tubes.

Preferably, the one or more apertures is/are arranged asymmetrically. Preferably, at least a portion of the outer perimeter is recessed, providing a gap to permit the passage of gas past the end plate when the perforating gun is assembled, to facilitate retrieval of the end plate and charge tube from the perforating gun barrel or to provide space for manipulation of the end plate and charge tube during assembly. Preferably, the plate member includes a passage to permit passage of an initiating device. Preferably, the passage comprises a central bore. Preferably, the alignment system includes an alignment tab extending from the outer perimeter of the plate member and a corresponding alignment groove within the inner circumference of the perforating gun barrel. Preferably, the end plate further includes an attachment system for attachment of an initiating device. Preferably, the attachment system comprises a puck adapted to attach to the end plate, the puck having a threaded aperture having a compression chamber, the aperture adapted to receive a compressible member and a threaded tube, wherein tightening the threaded tube into the threaded aperture compresses the compressible member in the compression chamber to frictionally engage the initiating device. Preferably, the compressible member is a cylindrical member having a central passage for passage of the initiating device or is an o-ring.

Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:

FIG. 1 is a perspective view of a perforating gun during loading in accordance with an embodiment of the invention;

FIG. 2 is a top view of an end plate in accordance with an embodiment of the invention;

FIG. 3 is a perspective view of an end plate, puck, and tube in accordance with an embodiment of the invention;

FIG. 3 a is a cross section of the puck in accordance with an embodiment of the invention; and

FIG. 4 is a perspective view of an end of a charge tube in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

Generally, the present invention provides a method and apparatus for assembling and loading perforating guns for downhole use. In particular, the present invention provides an end plate that can be produced at minimal cost, and that will prevent misalignment when used with one of a number of charge barrels of different design diameters for different applications.

With reference to FIG. 1, a perforating gun is shown during assembly. A plate member in the form of end plate 10 is attachable to the assembled charge tube 20, preferably by welding, which is slid into the perforating gun barrel 30. It is critical for proper operation that the charge tube 20 be properly substantially aligned in the perforating gun barrel 30 to line up the charges 21 with the weakened or scalloped portions 32 of the perforating gun barrel 30. The end plate 10, therefore, includes an alignment system in the form of alignment tab 11, and the perforating gun barrel 30 includes an alignment groove 31 such that the alignment tab 11 and the alignment groove 31 can be matingly engaged as the gun is loaded.

The alignment system may include alternate forms and configurations, for example, rather than an alignment tab 11 protuberant from the end plate 10, an adjustable set screw (not shown) may be adjustably protuberant from the end plate 10 to matingly engage the alignment groove 31 as the perforating gun barrel 30 is loaded.

In addition, the tongue/groove configuration may be reversed—e.g. the protuberant member may extend (not shown) from the perforating gun barrel 30 to matingly engage a groove (not shown) within the end plate 10. For example, referring to FIG. 2, the shape of alignment tab 11 extending without the outer perimeter 90 could instead be reversed to form a groove (not shown) extending within the outer perimeter 90. Typically, the perforating gun barrel 30 is threaded internally, and thus such a reversed configuration is more complicated. A protuberant member extending directly inward from the perforating gun barrel 30 to matingly engage a groove (not shown) within the end plate 10 would interfere with a typical threaded connection. In such a configuration, special threading or other means to avoid that interference could be utilized. Another option to provide a protuberant member extending from the perforating gun barrel 30 to matingly engage a groove (not shown) within the end plate 10 may be accomplished indirectly by including an intermediate member (not shown), such as an intermediate ring (not shown), the intermediate ring having an outer side adapted to mate with the perforating gun barrel 30 and an inner side adapted to provide a protuberant member extending from the inner side to matingly engage a groove (not shown) within the end plate 10.

As shown in FIG. 2, the end plate 10 has an outer perimeter, preferably an outer circumference 90, which is defined by a series of flanges 12, and an inner perimeter, preferably an inner circumference 91. Preferably, the inner circumference 91 provides a space or plate passage 100.

As shown in FIGS. 3 and 3 a, preferably, an attachment system for attachment of an initiating device in the form of a detonating cord 110 includes a puck 40 adapted to matingly engage the end plate 10. The puck 40 may be constructed of a phenolic material but may be constructed of any suitable material, for example a plastic or a resin. The puck 40, preferably includes prongs 41 for engaging the attachment points 14 of the end plate 10. The puck 40 generally serves as an alignment device or centralizer for an initiating device such as a primer cord or detonating cord 110, which initiates detonation triggered by a firing head when the system is used. In addition, the puck 40 receives a threaded member in the form of a tube 45 into a threaded aperture 47. The threaded aperture 47 includes a compression chamber 49. A compressible member 120 in the form of cylindrically shaped member 130 having a central passage or an o-ring 140 etc. may be inserted into the threaded aperture 47 to the compression chamber 49. The compression chamber 49 is configured such that the compressible member 120 is then compressed by the tube 45 as it is forced into the threaded aperture 47 (e.g. by threading), thereby causing the compressible member 120 to engage the initiating device such as detonating cord 110, providing a friction fit holding the detonating cord fixed in relation to the puck 40. As shown in FIG. 3 a, the compression chamber 49 may have a threaded inner surface, but it may also be smooth or otherwise configured. As shown in FIG. 3 a, the configuration of the compressible member 120 may vary greatly, and thus so may the compression chamber 49. As shown in FIG. 3 a, the compression chamber 49 is depicted to correspond to the cylindrically shaped member 130, and a shallower compression chamber 49 would be used in the case of an o-ring 140. An o-ring 140 could also be used instead at the interface between the shown threaded aperture 47 and the shown compression chamber 49.

Charge Tube

A typical charge tube 20 is shown in FIG. 4 in end view. The charge tube 20 includes at least one locating tab 22 extending from each end surface of the charge tube 20. As shown, the charge tube 20 may include a plurality of locating tabs 22, such as three locating tabs 22. Once the charge tube 20 is loaded with the charges 21, the locating tabs 22 are aligned with appropriate alignment apertures 15, 16, 17, or 18 within the end plate 10, depending on the size of the charge tube 20, to mate the charge tube 20 and the end plate 10. As shown, each one of alignment apertures 15, 16, 17, or 18 are representative of alignment apertures which are adapted to align and mate with a charge tube 20 of a different size (diameter), e.g. in order of increasing size alignment apertures 15, 16, 17, 18. The end plate 10 is then welded in place or otherwise secured to the charge tube 20.

A locating tab 22 is critical to ensure that the charge tube 20 is properly aligned with the end plate 10. Proper alignment of the end plate 10 will ensure that the charge tube 20 is correctly oriented within the perforating gun barrel 30 due to the alignment tab 11 on the end plate 10, which mates with the alignment groove 31 in the threaded portion of the perforating gun barrel 30. A variety of methods are known for threading and attaching initiating devices to the charge tube 20. Accordingly, the end plate 10 may be modified to attach to suit these methods. The end plate 10 may be retained in the perforating gun barrel 30 through the use of a retainer known in the art, such as a snap ring (not shown).

The alignment tab 11 and alignment groove 31 may be reversed, i.e. the alignment tab 11 may extend (directly or indirectly) from the perforating gun barrel 30 and the end plate 10 may have an alignment groove 31.

As an additional safeguard against misalignment, the locating tabs 22 may be arranged asymmetrically around the end of the charge tube 20. More specifically, if misalignment is a concern then the locating tabs 22 should be arranged around the end of the charge tube 20 at unequal intervals. The apertures in the end plate 10 should mirror the arrangement of the locating tabs 22 on the charge tube 20 of each diameter. This asymmetry will ensure that a particular charge tube 20 can only be attached to the end plate 10 in one predesigned orientation—the orientation which will ensure correct alignment with the charge tube 20 and thus alignment of the charges 21 with the weakened or scalloped portion 32 on the perforating gun barrel 30.

Universal End Plate

As noted above, the end plate 10 includes a series of apertures 15, 16, 17, 18, which may be engaged by the locating tab 22 on a charge tube 20. It is understood that an end plate 10 in accordance with the invention need only have one aperture for permitting locating of one size of charge tube, however, this would require a separate end plate 10 for each size of charge tube 20. The end plate 10 shown in FIG. 2 is universal in that for a given outer diameter (corresponding to a certain size of perforating gun barrel), the end plate 10 can be used with any one of a number of sizes of charge tube 20. This minimizes the inventory of end plate 10 types which must be maintained.

When the end plate 10 is affixed to the charge tube 20, it is preferable that the end plate 10 be welded or otherwise securely fastened to the charge tube 20. This will ensure the integrity of the assembled gun, preventing accidental dislocation of parts or misalignment, which occurs with present systems. Attachment by deformation of locating tabs 22 is possible, but generally discouraged as it is considered insecure. In addition, the present end plate 10 is simpler to manufacture than previous end collars in that the end plate 10 can be laser-cut from a single piece of steel, rather than manufacturing with expensive molds or machined.

As well, misalignment and shearing of the alignment tab 11 will not occur with the present end plate 10 due to the composition of the steel disk, compared with previous softer aluminum end collars, and the steel disks can be easily manufactured from a variety of sheet metal products without expensive dies or molds.

The end plate 10 shown in FIG. 2 includes flanges 12 extending to form the outer perimeter or circumference. It is also contemplated that the end plate 10 could have a complete outer circumference (in other words, it could be round), however the pictured configuration has certain inherent advantages and is the preferred embodiment. For example, a space or gap is provided between the flanges 12 to allow the end plate 10 to be held securely by the hand and fingers of the worker doing the assembly during placement of the charge tube 20 within the perforating gun barrel 30. In addition, the space is useful for retrieval if the charge tube 20 must be removed from the perforating gun barrel 30; and permits pry bars or other tools to be used to manipulate or lever the device apart or into alignment. As well, the space allows for the passage of air and gases past the end plate 10 during the explosion of the perforating charges.

Engagement of End Plate with the Perforating Gun Barrel

As described previously, the end plate 10 is designed to engage the perforating gun barrel 30 in a specific orientation. As shown in FIG. 1, the end plate 10 includes at least one alignment tab 11, and the perforating gun barrel 30 includes an alignment groove 31 for receiving the alignment tab 11. When the charge tube 20 with fixed end plate 10 is ready for insertion into the perforating gun barrel 30, the assembler will grasp the end plate 10 at the spaces between the flanges 12, and will rotate the end plate 10 such that the alignment tab 11 is in line with the corresponding alignment groove 31 in the perforating gun barrel 30. With the present end plate 10, the assembler can maintain a firm grasp on the end plate 10 during the entire insertion process. In past systems, this has not been possible, as previous end collars and end plates have not included manipulation space. As such, previous charge tubes 20 would be initially aligned with the perforating gun barrel 30, and the charge tube 20 would then be pushed into place without ensuring that proper alignment was maintained. Due to the mass of the components, this often resulted in stripping the interior surface or threading of the perforating gun barrel 30, or shearing of any alignment mechanism, and then with misfiring or gun failure being the result. The present alignment system (exemplified by the above tab and groove) may include any equivalent method for aligning the end plate 10 within the perforating gun barrel 30. It is only important that the end plate 10 act as an alignment system between the perforating gun barrel 30 and the charge tube, ensuring that the explosive perforating charges are properly aligned with the weakened portions of the perforating gun barrel 30.

With the present end plate 10, the charge tube 20 can include a welded or otherwise affixed end plate 10 at each end of the charge tube 20, providing further ease of alignment. The end plate 10 at the first-inserted end of the charge tube 20 may not include an alignment tab 11, so as to slide past the threads at the collar of the perforating gun barrel 30 and toward the other end of the barrel. Alternatively, a simplified end plate 10, such as a simple centralizer, could be affixed to the opposite end of the charge tube 20.

The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto. 

1. An end plate for use in the assembly of a perforating gun, the end plate comprising: (a) a plate member having an outer perimeter adapted to be slideable within a perforating gun barrel; and (b) an alignment system without the outer perimeter adapted for mating in specific orientation with the inner surface of the perforating gun barrel, the plate member having one or more alignment apertures for aligning and mating with one or more corresponding locating tabs of a charge tube.
 2. The end plate of claim 1, wherein the one or more alignment apertures are arranged asymmetrically.
 3. The end plate of claim 1 wherein a portion of the outer perimeter is recessed, providing a gap to permit the passage of gas past the end plate when the perforating gun is assembled, to facilitate retrieval of the end plate and charge tube from the perforating gun barrel, or to ease manipulation during assembly or disassembly.
 4. The end plate of claim 1, wherein the one or more alignment apertures comprise a series of apertures for mating with the locating tabs of one of a variety of sized charge tubes.
 5. The end plate of claim 1, wherein the plate member comprises a plate passage to permit passage of an initiating device.
 6. The end plate of claim 5, wherein the passage comprises a central bore.
 7. The end plate of claim 5, wherein the initiating device comprises a detonating cord.
 8. The end plate of claim 1, wherein the alignment system comprises an alignment tab extending from the outer perimeter of the plate member and a corresponding alignment groove within the inner circumference of the perforating gun barrel.
 9. The end plate of claim 1, further comprising an attachment system for attachment of an initiating device.
 10. The end plate of claim 9, wherein the attachment system comprises a puck adapted to attach to the end plate, the puck having a threaded aperture having a compression chamber, the aperture adapted to receive a compressible member and a threaded tube, wherein tightening the threaded tube into the threaded aperture compresses the compressible member in the compression chamber to frictionally engage the initiating device.
 11. The end plate of claim 10, wherein the initiating device comprises a detonating cord.
 12. The end plate of claim 10, wherein the compressible member is a cylindrical member having a central passage for passage of the initiating device, or is an o-ring.
 13. A process for assembling a perforating gun comprising the steps of obtaining a charge tube with open ends, the charge tube loaded with charges and having an arrangement of locating tabs on at least one of the open ends; providing an end plate slideable within a perforating gun barrel and having a corresponding arrangement of alignment apertures for mating with the locating tabs, the end plate also having an alignment system for mating in specific orientation with the inner surface of a perforating gun barrel; affixing the end plate against the end of the charge tube such that the locating tabs mate with the alignment apertures; and inserting the charge tube and end plate into the perforating gun barrel such that the alignment system properly orients the end plate and the charge tube within the perforating gun barrel to align the charges with weakened or scalloped portions of the perforating gun barrel.
 14. The process of claim 13, wherein the arrangement of locating tabs is asymmetrical.
 15. A universal end plate for use in the assembly of a perforating gun, the end plate comprising: (a) a plate member having an outer perimeter slideable within a perforating gun barrel; and (b) an alignment system without the outer circumference for mating in specific orientation with the inner surface of the perforating gun barrel, the plate member having at least two sets of alignment apertures, each set of apertures including one or more apertures for mating with corresponding locating tabs of one of a variety of sized charge tubes.
 16. The end plate of claim 15, wherein the one or more apertures is/are arranged asymmetrically.
 17. The end plate of claim 15, wherein at least a portion of the outer perimeter is recessed, providing a gap to permit the passage of gas past the end plate when the perforating gun is assembled, or to facilitate retrieval of the end plate and charge tube from the perforating gun barrel.
 18. The end plate of claim 15, wherein the plate member includes a passage to permit passage of an initiating device.
 19. The end plate of claim 18, wherein the passage comprises a central bore.
 20. The end plate of claim 15, wherein the alignment system includes an alignment tab extending from the outer perimeter of the plate member and a corresponding alignment groove within the inner circumference of the perforating gun barrel.
 21. The end plate of claim 15, further comprising an attachment system for attachment of an initiating device.
 22. The end plate of claim 21, wherein the attachment system comprises a puck adapted to attach to the end plate, the puck having a threaded aperture having a compression chamber, the aperture adapted to receive a compressible member and a threaded tube, wherein tightening the threaded tube into the threaded aperture compresses the compressible member in the compression chamber to frictionally engage the initiating device.
 23. The end plate of claim 22, wherein the compressible member is a cylindrical member having a central passage for passage of the initiating device or is an o-ring. 